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- Author or Editor: M.P. Pritts x
The main effects and interactions of soil-applied P, B, and Zn on yield and its components were examined in the field at two pH levels with `Earliglow' strawberries (Fragaria × ananassa Duch.). Applied nutrients had significant effects on several yield components, but responses depended on the levels of other nutrients or the soil pH At a soil pH of 5.5, yield responded linearly to B and quadratically to P. At pH 6.5, P interacted with B and Zn. Fruit count per inflorescence was the yield component most strongly associated with yield followed by individual fruit weight. However, these two yield components responded differently to soil-applied nutrients. Foliar nutrient levels generally did not increase with the amount of applied nutrient, but often an applied nutrient had a strong effect on the level of another nutrient. Leaf nutrient levels were often correlated with fruit levels, but foliar and fruit levels at harvest were not related to reproductive performance. Our study identifies some of the problems inherent in using foliar nutrient levels to predict a yield response and demonstrates how plant responses to single nutrients depend on soil chemistry and the presence of other nutrients.
Plants of chrysanthemum (Dendranthema grandiflora Tzvelev.) were grown under one of 25 irradiance and temperature combinations from start of short days to flower. Four phases of development were defined as 1) the start of short days to the appearance of 4-mm terminal flower buds (phase I), 2) appearance of 4-mm terminal flower buds to removal of lateral flower buds when the terminal flower bud was 7 to 8 mm (phase II), 3) removal of lateral flower buds to flower buds showing first color (phase III), and 4) flower buds showing color to flowering (phase IV). Path analysis was used to study the influence of development time and relative dry weight gain during each of these four phases on development time and relative dry weight gain of subsequent phases. Relative dry matter accumulation during phases I, II, III, and IV significantly influenced cumulative relative dry weight gain, with phase I having the greatest influence. Increasing relative dry weight gain during phase I had a significant negative effect on relative dry weight gain in phase II. Time within each phase significantly affected total time to flower. Under the constant environmental conditions of this experiment, time in one phase did not influence the length of time in later phases.
Several genotypes of Vactinium angustifolium were taken at random from 17 environmentally diverse sites in Michigan and transplanted to a common greenhouse environment. During the 2nd season of growth, genotypes from southern sites exhibited significantly greater numbers of inflorescence buds than northern sites. Genotypes from sites with low light levels exhibited greater numbers of inflorescence buds and flowers per bud than those from sites with high light levels. Genotypes from dry sites produced larger fruit than genotypes from wet sites. These data suggest that environments exist in which natural selection has favored horticulturally desirable traits.
A mixed cultivar blueberry planting was treated with a concentrated sucrose solution before fruit ripening and after episodes of rain during the harvest season. Fruit losses due to birds were monitored throughout the season in this planting and in the same cultivar in a separate nontreated planting ≈200 m (650 ft.) away. Fruit loss to birds was ≈50% greater in the nontreated planting over the first 3 weeks of harvest. In addition, bird activity was monitored between 0600 and 0700 hr on two occasions in each planting during the early harvest season. Bird activity was many times higher in the nontreated planting. These observations suggest that sucrose should be tested more widely for potential activity on bird feeding behavior.
Phytophthora is a severe root rot disease in most raspberry production regions throughout the world. Disease control options are limited to raised bed culture and fungicide applications. Few Phytophthora-resistant varieties are available that have commercial quality. Little is known about how soil amendments (i.e., composts, fertilizers, and limestones) influence Phytophthora control in raspberry. We evaluated the effects of preplant soil modification on the incidence of Phytophthora root rot in red raspberries. The experiment was conducted simultaneously at two sites to differentiate between the nutritional value of the amendments and the disease control value. One site has a known history of Phytophthora and a the second site is assumed to be free of the causal organism. Raspberry plant growth and fruit yield measurements were taken for all treatments. Preplant soil application of Gypsum (CaSo4) and post-plant applications of phosphorous acid sprays (H3PO3) had the greatest fruit yields compared to all other treatments in the Phytophthora-infested site. Gypsum-treated plots had greater cane diameter, cane height, and cane density compared to the control plots on the Phytophthorainfested site. A second experiment was conducted to further investigate the use of gypsum for control of Phytophthora in raspberries. Field soil was collected for use as potting medium from each of the aforementioned sites and pathogen free `Titan' plants were established in the greenhouse. After subsequent floodings, gypsum-treated soils delayed foliar disease symptoms compared to the control plots. At the end of the experiment, the control plants had 100% foliar disease symptoms and gypsum-treated pots had 33% disease symptoms. This study suggests that gypsum could be used in an integrated approach to Phytophthora management in raspberries. Future research should identify minimal effective rates of gypsum, examine other calcium sources, and determine effectiveness in other fruit crops.
Blueberry shoestring virus (BBSSV) is the most serious disease in Michigan, and it has been reported in New Jersey, Washington, North Carolina, and Nova Scotia (4, 8). Shoestring is particularly difficult to eradicate, since there is no known control other than removing diseased bushes, and infected bushes do not show external symptoms for up to 4 years. Also, no cultivars of highbush blueberry are immune to the disease (2).
Flower bud injury was assessed in 18 cultivars of highbush blueberry (Vaccinium corymbosum L.) after two spring frosts. Bud position on shoots was significantly correlated (P < 0.05) with percent brown ovaries. Significant differences in proportion of brown ovaries were noted among cultivars, but most of the variation was associated with stage of bud development. The least-developed buds were the most hardy. Bloom date was significantly correlated with harvest date across cultivars, although ‘Spartan’ flowered much later than other early ripening cultivars.
Sixteen cultivars of blueberry (Vaccinium corymbosum L.) were field screened for resistance to the blueberry aphid Illinoia pepperi (McGillivary), the vector of blueberry shoestring virus. Significant differences were observed with ‘Bluejay’, ‘Northland’, ‘Bluetta’ and ‘Bluehaven’ supporting the lowest numbers, while ‘Spartan’, ‘Darrow’, ‘Lateblue’, ‘Coville’ and ‘Jersey’ carried the highest numbers. There was no significant correlation between aphid number and new shoot number, percentage of shoots with new growth, length of new growth, leaf length or leaf width. Half of the aphids were found in the lower 1/3 of the bushes.
Flower bud and leaf samples collected from a wide range of native North American Vaccinium populations were tested for the presence of blueberry shoestring virus (BBSSV) using the enzyme-linked immunosorbant assay. The highest disease incidence was found in Michigan (14%), although a few positive samples also were found in Virginia, New Jersey, Maine, Ontario, and Quebec. Of seven species tested, only V. corymbosum L. and V. angustifolium Ait. were infected with BBSSV.